1. Field of the Invention
The present invention generally relates to a clean air room for use in a semiconductor factory, which can maintain an ultra clean air environment.
2. Description of the Prior Art
In a semiconductor factory, a clean air room or ultra clean environment is required to improve the technique for manufacturing semiconductor devices such as large-scale or very large scale integration.
The provision of such a clean air room is also important in order to improve fully automated systems, automatic transfer systems or unmanned manufacturing lines.
A conventional clean air room typically includes a clean air chamber, the top wall of which has a laminar air flow system with special air filters (HEPA filter) and an air blower system for supplying pressurized air. The air is introduced into the clean air chamber through the air filters and then, circulated therein. The degree of cleanliness in a room is represented by the number of particles of dust or other impurities per one cubic feet, for example at Class 1, Class 100 or Class 1000. The smaller the number, the cleaner the room environment. Class is a function of atmospheric pressure, velocity and filtration capability.
FIG. 6 illustrates a conventional clean air room (U.S. Pat. No. 4,699,640).
The prior art clean air room includes three different sections, upper section 2, middle section and lower section 3. The middle section has two side walls 4, 4 and two hanging partitions 5, 5 having openings and cooperating with the side walls 4, 4 to form three clean zones or clean air chambers R.sub.1, R.sub.2 and R.sub.3.
The chamber environment is maintained as follows. An air conditioning equipment 6, placed adjacent to the lower section 3, is active to draw air from the lower section 3 and feed the air under pressure to the upper section 2 through an external feed pipe 14. The air vertically flows from HEPA filters 8 mounted on a top wall 7 to vent holes 10 as shown by the arrow.
Each of the clean air chambers R.sub.1 has a transfer robot 11 and a processing station 12a of a semiconductor manufacturing apparatus 12. Its degree of cleanliness is maintained at Class 100 or cleaner. The rest of each of the semiconductor manufacturing apparatus 12 extends through the opening of the hanging partition 5 and is located within the clean air chamber R.sub.2. Its degree of cleanliness is maintained at Class 1000 or dirtier since wafers need not be exposed. The degree of cleanliness of the clean air chamber R.sub.3, where an operator works, is on the order of lowest Class 10,000. The three clean air chambers share the air supply chamber or upper section 2 and the air returning chamber or lower section 3.
The hanging partition 5, made of plastic, is in the form of an antistatic plate and has a lower end located 20 to 30 m above the apparatus 12. The cleanliness of each zone varies depending upon the specifications and number of the HEPA filters 8 and how many times an hour each zone is ventilated.
Power cords, wires and pipes are all contained in the lower section 3 so as to effectively utilize the clean air room.
With the clean air room thus constructed, the cleanliness of the clean air chambers varies depending on operating conditions. This system consumes less energy, maintains cleaner air environment and is inexpensive to maintain.
A disadvantage with the prior art clean air room is that the direction of flow of air in the clean air chambers cannot be independently controlled. This is because a single large air conditioning equipment is used to provide a constant flow of air to the air supply chamber or the upper section of the clean air room. This type of air conditioning equipment requires a considerable amount of energy and suffers from mechanical failure. Such failure adversely affects the overall clean air room. Consequently, it is difficult to maintain the clean air room, particularly clean air chamber R.sub.1, in a clean air condition for a long period of time.
Also, a fan of the air conditioning equipment is spaced away from the clean air chamber, and a long pipe must be used to supply air to the clean air chamber. This arrangement results in a decrease in the air pressure and thus, requires a larger air conditioning equipment.